The transactive memory system (TMS) has been considered as one critical element for effective teamwork. However, viewing TMS as a second‐order construct that mixes cognitive (specialty and credibility) and behavioural (coordination) components leads to confusion and increases the difficulty in interpreting study results. This study follows the concept proposed by one recent study and attempts to distinguish between behavioural and cognitive components. Furthermore, drawing on the need for diverse members to be integrated behaviourally, we also attempt to extend the TMS research stream by proposing a more comprehensive behavioural component of TMS. We argue that to obtain better teamwork outcomes, information system development (ISD) team members need to integrate the expertise possessed by each individual, make decisions jointly and interlink all individual actions. In light of this, our study aims to replace coordination with team behavioural integration, a more comprehensive behavioural consequence of cognition and explore the critical role of behavioural integration in ISD teams by understanding its impact on ISD teamwork project team performance. The study result, based on data collected from 205 information system project managers, supports our hypotheses that expertise specialty, credibility and their interaction positively affect team behavioural integration. This, in turn, leads to enhanced project team performance.